Flicker screen effect
The flickering effect can be achieved by adding an effect strip on top of the movie clip. 


Shift+A > Effect Strip > Color
Go to the Properties Panel of the video sequence editor (N) 
Set the blendtype to Alpha Over
Set a keyframe on the opacity (also in Properties Panel) by clicking on I
Go to the graph editor and add a Noise Modifier (in the Properties Panel of the graph editor) 
Tweak the different options in the Noise Editor like scaling, strength, phase the frame range etc.